Study of the pressure effects in TiOCl by ab initio calculations

Electronic structure calculations on the low-dimensional spin-1/2 compound TiOCl were performed at several pressures in the orthorhombic phase, finding that the structure is quasi-one-dimensional. The Ti3+ (d(1)) ions have one t(2g) orbital occupied (d(yz)) with a large hopping integral along the b-direction of the crystal. The most important magnetic coupling is Ti-Ti along the b-axis. The transition temperature (T-c) has a linear evolution with pressure, and at about to 10 GPa this T-c is close to room temperature, leading to a room temperature spin-Peierls insulator-insulator transition, with an important reduction of the charge gap in agreement with the experiment. On the high-pressure monoclinic phase, TiOCl presents two possible dimerized structures with along or short dimerization. Long dimerized state occurs above 15 GPa, and below this pressure the short dimerized structure is the more stable phase. (C) 2009 Elsevier B.V. All rights reserved.